1. Field of the Invention
The present invention relates to a multilayer capacitor wherein the equivalent serial inductance (ESL) is greatly reduced, more particularly relates to a multilayer ceramic capacitor capable of reducing the voltage fluctuations of a CPU power source.
2. Description of the Related Art
In recent years, CPUs (central processing units) used for data processing apparatuses have become higher in operating frequency and remarkably increased in current consumption due to the improvement in processing speeds and higher integration. Along with this, there is a trend toward reduction of the power consumption so as to reduce the operating voltage. Therefore, in power sources for supplying power to CPUs, faster and larger current fluctuations occur. It has become extremely difficult to keep voltage fluctuations accompanying current fluctuations to within tolerances of the power sources.
Therefore, as shown in FIG. 7, a multilayer capacitor 100 called a “decoupling capacitor” is connected to a power source 102 and frequently used for stabilization of the power source. Further, by fast charging and discharging at the time of high speed, transient fluctuations in current, the multilayer capacitor 100 supplies current to the CPU 104 and suppresses voltage fluctuations in the power source 102.
Along with the increasingly higher operating frequencies of today's CPUs, however, the current fluctuations have become faster and larger. Therefore, the equivalent serial inductance (ESL) of the multilayer capacitor 100 itself shown in FIG. 7 becomes relatively larger. As a result, the equivalent serial inductance greatly influences voltage fluctuations of the power source.
That is, in a conventional multilayer capacitor 100 used for the power source circuit of the CPU 104 shown in FIG. 7, the ESL of the parasitic part shown in the equivalent circuit of FIG. 7 is high. Thus, along with fluctuations of the current I as shown in FIG. 8, the ESL inhibits the charging and discharging of the multilayer capacitor 100. Therefore, in the same way as the above, the fluctuations in the voltage V of the power source easily become greater as shown in FIG. 8, so that it will become impossible to handle the increasingly higher speeds of CPUs in the future.
This is because the voltage fluctuations at the time of charging and discharging as transition of the current are approximated by the following equation 1 and therefore the level of the ESL is related to the magnitude of fluctuation of the power source voltage:dV=ESL·di/dt  formula (1)
Here, dV is transitory fluctuation of voltage (V), “i” is the amount of current fluctuation (A), and “t” is the time of fluctuation (sec).
Here, the appearance of this conventional capacitor is shown in FIG. 9 and the internal structure is shown in FIG. 10. Below, a conventional multilayer capacitor 100 will be explained based on these figures. That is, the conventional multilayer capacitor 100 shown in FIG. 9 is structured to give an electrostatic capacity by alternately stacking a pair of ceramic layers 112A each provided with one of two types of internal conductor layers 114 and 116 shown in FIG. 10 and forming a dielectric body 112.
Further, these two types of internal conductor layers 114 and 116 are led out to mutually facing two side surfaces 112B and 112C. Further, the terminal electrode 118 connected to the internal conductor layers 114 and the terminal electrode 120 connected to the internal conductor layer 116 are set at the mutually facing side surfaces 112B and 112C of the multilayer capacitor 100 shown in FIG. 9.
In the conventional multilayer capacitor 100, the ESL is large and it has been particularly difficult to reduce the voltage fluctuations of CPU power sources.
Note that to reduce the ESL, multilayer capacitors disclosed in the Japanese Unexamined Patent Publication No. 11-144996, No. 2001-284171, No. 2002-151349, No. 2002-231559 and No. 2002-164256, etc. have been developed.
However, there have been demands for multilayer capacitors capable of furthermore reducing particularly the voltage fluctuations of CPU power sources.